1. Field of the Invention
This invention relates generally to sports or recreational vehicles of the type which may be driven off the road, and more specifically to a vehicle incorporating a limited-type differential whereby the maneuverability of the vehicle, including its starting and stopping is enhanced.
2. Discussion of the Prior Art
Over the past decade or so there has been a great upsurge in the popularity of motor vehicles which may be operated over rough terrain, in snow or on ice, or on blacktop pavement as well. Typical of such a vehicle in which the present invention finds use is the TRI-MOTO.RTM. three-wheeled motorized unit manufactured and sold by Yamaha Motor Company, Ltd. of Japan. This vehicle comprises a frame having a front fork which supports a single, relatively large size, inflatable balloon tire which may be turned for steering purposes by means of handlebars. The two rear wheels are mounted on a common axle and the axle carries a sprocket which is chain-driven by a motor also carried by the frame.
In this prior art three-wheeled vehicle identified above, a problem is often encountered in cornering. That is, when it desired to round a corner, the driver must be sufficiently skilled and familiar with the use of the vehicle to lean properly toward the outside wheel. The natural tendency is for an untrained driver to lean into the turn, but such a maneuver is ineffective and actually makes turning more difficult. As a result, tire wear is increased and the ground surface on which the vehicle is being used will be scuffed.
One solution to the foregoing problem is to replace the fixed single axle arrangement with a double axle, the two axles being joined by a conventional differential gear train. When using a such differential gear train during a turn, the inside wheel and outside wheel are able to rotate at different speeds, thus facilitating the turning operation. However, in an all-terrain vehicle of the type described, a conventional differential presents other problems that render its use impractical. As is well-known in the art, with a conventional differential gear train joining the two axles, if one wheel is free to spin, such as might occur in snow or on ice or when traveling through sand or mud, the other wheel loses traction. Thus, the vehicle will tend to become mired.
The KLT three-wheeled vehicle manufactured by the Kawasaki Company uses a dual mode differential in coupling the two rear axles together. Thus, when driving on dry pavement or solid ground, the unit functions as a standard differential, thus accommodating the steering and cornering. Should the vehicle become bogged down either in sand, mud, or snow, the driver may choose to turn off the engine, dismount from the vehicle and use a special wrench on the differential to lock the two axles together so that the unit functions as a single axle and providing the desired torque on each wheel to allow it to be moved from its mired condition.
In accordance with the teachings of the present invention, the drawbacks of the prior art are obviated through the use of a limited differential, preferrably of the torque transfer type. When such a device is used for coupling the two rear axles together, more of the torque or driving force is applied to the wheel which is turning at the lower rotational velocity. Thus, when cornering, the majority of the driving torque is applied to the inside wheel and the outside wheel turns freely at a rate determined by the vehicle's speed and the turning radius involved. Thus, steering and maneuverability typical of a standard differential drive is provided. In the event that the vehicle encounters soft ground or snow and ice, and a torque transfer type limited differential is used, should one wheel begin to spin, all of the driving torque is automatically transferred to the wheel which happens to be moving at a lower angular velocity. Thus, power is supplied to one wheel or the other or to both automatically, depending on whether they are rotating at different speeds or at the same speed respectively.
The use of a torque transfer type limited differential affords still a further advantage as it relates to the braking of the vehicle. When using a standard differential, it is necessary to provide drum shoes or disc and caliper brakes on each of the two axles if stopping without pulling to one side is to be accomplished. When using a torque transfer type differential unit as in the present invention, only a single disc and caliper assembly is required. Upon application of the brakes, the braking force will be applied either uniformly to both wheels, provided they are both moving at the same rotational velocity, or to the particular wheel which is moving at the slower rotational velocity. Then, when speed equilibrium between the two wheels is reached, the applied braking force is distributed equally between the two wheels.